1. Field of the Invention
This invention relates to exhaust systems, and more particularly to apparatuses, systems, and methods for cooling exhaust gas as it leaves an enclosed exhaust stream.
2. Description of the Related Art
This patent application is related to patent application serial number <serial number> titled “Lobed Exhaust Diffuser Apparatus, System, and Method,” filed on the same date as the present patent application, and which is incorporated herein in its entirety.
Environmental regulations are becoming increasingly strict with regard to engine exhaust emissions such as nitrogen oxides (NOx) and particulate matter. In the United States, the U.S. Environmental Protection Agency will begin enforcing new, more stringent, environmental regulations with regard to diesel engine particulate emissions in 2007, which has occasioned the need for diesel particulate filters and/or other exhaust treatment devices such as NOx adsorbers to be placed in the exhaust stream before the exhaust is permitted to enter the atmosphere.
In most cases, an exhaust treatment system must initiate regeneration of particulate filters, NOx adsorbers, and other exhaust treatment devices from time to time as the devices fill up with soot, NOx, or the like. In the case of a particulate filter, as one example, this is done by increasing the temperature of the filter to a level where the soot is oxidized, above 400 C, and maintaining that temperature for several minutes or longer, depending on circumstances including the size of the filter, the amount of soot on the filter, the uniformity level of the soot, etc.
The high filter temperatures required for regenerations of this type increase the temperature of the exhaust, particularly at stationary or low-speed operation, meaning the exhaust leaves the tailpipe of the vehicle at a much higher temperature than it would during normal operation. This creates a potential safety hazard with regard to the heat flux of the gases leaving the tailpipe and creating discomfort or injury to humans, animals, or plants in proximity. It also increases the surface temperature of exhaust train components.
One way to deal with the problem would be to warn the operator of the vehicle or machine in which the engine and exhaust treatment system is installed of expelled exhaust temperatures reaching dangerous levels, enabling the operator to take steps to mitigate the situation, such steps potentially including moving the apparatus away from sensitive objects, initiating a cooling procedure, etc. This, however, would require detailed and expensive sensors and controls, would require operator intervention, and in any case the mitigation options for the operator would be relatively limited. If possible, it would be better that the exhaust gas be continually cooled before or as it leaves the tailpipe such that its temperatures never reach dangerous levels in the first place.
Treating exhaust to mitigate harmful consequences is nothing new, of course: mufflers and resonance filters have existed for decades for sound mitigation, and catalyst filters, particulate filters and the like have been and are being developed for substance emission control. The general problem of heat mitigation as the exhaust enters the atmosphere, however, is a relatively new one requiring novel approaches. The problem has been addressed in certain limited circumstances, such as exhaust temperature mitigation of fire trucks when they are pumping water. Some fire trucks (though not all) are equipped with a water spray device at the exhaust outlet for exhaust cooling, but such a scheme is limited to a situation where there is a ready water supply as well as experienced firefighters with hoses in hand rather than a single machine operator inexperienced in such situations.
From the foregoing discussion, it should be apparent that a need exists for cooling exhaust gases as they leave the tailpipe of an engine-driven machine, particularly one containing a diesel engine and particulate filter or other treatment device requiring regeneration. Certain types of vocational vehicles not using the emissions control devices discussed above can also benefit from cooled exhaust gases.